The invention relates to a motor vehicle with an automatic transmission and an overrunning clutch used as a hill support. A motor vehicle of the generic type is described in terms of its basic mode of operation in German Offenlegungsschrift 2,003,977.
The object of the present invention is to ensure automatically the necessary non-positive connection in the automatic transmission by appropriate control of the working pressure applied to shift elements (clutches, brakes) working by frictional engagement, whenever hill support is to be employed.
This object is achieved advantageously according to the invention, in which the overrunning clutch can be arranged in a hydrodynamic torque converter, and can prevent the turbine from rotating backwards. To guarantee the hill-support torque required for a particular vehicle, the so-called shift plate receiving the hydraulic controls can be widened correspondingly. Since no simple signal is available to indicate when the hill support is required, the control is such that, below a measurable minimum vehicle speed (minimum value of the transmission output speed), the working pressure is raised sufficiently high that the desired hill support is guaranteed. So that the output of the following transmission parts does not also rotate in the opposite direction to the gear shift, the control members transmitting the torque by non-positive connection are excited to a correspondingly high degree.
These functions can, for example, be performed hydraulically. A first switch position "drive" or "neutral" is obtained by means of the conventional range selector slide. In a second switch, the working pressure corresponding to the torque can be compared with the pressure required for hill support. This is carried out in a valve slide. If the working pressure is lower than the pressure for hill support, a speed comparison is carried out in a third switch with regard to the output speed by means of a slide. If the speed is below no, the pressure is increased to the pressure for the hill support. The hill support is then automatically provided when it is required.
In electronic control, the current signal for the torque-dependent working pressure and the electrical speed signals go directly to electronic switches and from there to the proportional solenoid valve controlling the working pressure. All intermediate stages between purely hydraulic and fully electronic control are of course possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.